1. Field of the Invention
This invention relates to a method of preparing a coated abrasive article and, more particularly, a method for preparing a coated abrasive article in which the presence of multiple layers of abrasive grains are minimized.
2. Discussion of the Art
Coated abrasive articles generally comprise a flexible backing having a coating of abrasive grains on one major surface thereof. Coated abrasive articles typically employ a make coat, e.g., a resinous binder, in order to secure the abrasive grains to the backing, and a size coat, e.g., a resinous binder, which is applied over the make coat and abrasive grains in order to firmly bond the abrasive grains to the backing. In certain situations, it is desired to have only one layer of abrasive grains bonded to the backing. Additionally, it is also frequently desired to have the sharp ends of the abrasive grains oriented away from the backing to optimize cut rate.
In the typical manufacturing process for preparing coated abrasive articles, a make coat precursor is first applied to the backing, the abrasive grains are then electrostatically projected into the make coat precursor, and the make coat precursor is partially cured in order to set the abrasive grains. Next, a size coat precursor is applied over the abrasive grains and make coat precursor, and, finally, the make coat precursor and size coat precursor are fully cured. When coating fine abrasive grains, multiple layers of abrasive grains tend to be applied during the electrostatic projecting step. In some instances, up to seven layers of abrasive grains are applied. The presence of multiple layers of abrasive grains becomes a more serious problem as the particle size of the abrasive grains is decreased. If the coating weight of the abrasive grains is reduced, a very blotchy, non-uniform coating of multiple layers of abrasive grains frequently results.
There are many disadvantages associated with multiple layers of abrasive grains in a coated abrasive article. First, many of the abrasive grains tend to be oriented so that their sharp ends do not project away from the backing. Second, abrasive grains tend to lay on top of one another, resulting in reduced abrading performance. Third, multiple layers of abrasive grains often reduce the flexibility of the coated abrasive article. Fourth, multiple layers increase the cost of the coated abrasive article.
U.S. Pat. No. 2,015,658 discloses a method of preparing abrasive articles by applying the make coat precursor by means of metered roll. However, this method does not allow for the abrasive grains to be oriented or electrostatically coated.